1. Field of The Invention
The present invention relates to a mark reading device in which the output beam of a laser oscillating device is applied to an object to scan the surface thereof. The laser beam reflected therefrom is received, at a light detection device, to read marks such as characters, bar codes, or the like.
2. Description of Related Art
The recent widespread use of computers has spurred the development and use of input devices such as character readers, bar code readers and the like. Such input devices are typically held in the operators hand for convenience and flexibility. Because of this, exact positioning and orientation are not possible. Thus, the reading device must be able to read over a wide range of distances and orientation angles to be reliable and practical. Previous mark reading devices have proved unreliable at reading surfaces at varying distances and angles. The laser output energy of such devices is fixed while in the scan mode. Consequently, the energy of laser light received at the detector is a function of the distance between the reading device and the surface to be read and the incident angle of the surface relative to the laser beam. When such a device is too close to the surface that is to be read the detection device is saturated and the device fails to function. When the same device is too far away from, or at a high angle to, the surface that is to be read the reflected signal at the detection device is too low and again the device fails.
The typical mark reading device found in the prior art consists of a laser oscillating device, a rotatable mirror for deflecting the laser beam output of the oscillating device through a predetermined scan angle, a light detection device for receiving the reflected laser beam and signal processing circuitry. The above elements can be incorporated into a stationary housing, a portable housing such as a "gun" configuration, or the like.